P a r tia l p r e s s u r e s o f o x y g e n a n d c a r b o n d i o x i d e
d u r i n g e x t e r n a l a n d in t e r n a l r e s p i r a t i o n
F ig u r e 1 3 . 5
The changes in partial pressures of oxygen and carbon dioxide drive the diffusion of
these gases in external and internal respiration. The partial pressures of various gases
in the atmosphere are listed for comparison.
Gas exchange between atm osphere '
and alveoli:
Partial
pressures in atm osphere:
»
Atmospheric PO
greater than alveolar PO
»
Atmospheric PC0 less than alveolar PCC
,2
Deoxygenated blood:
PO
= 40 mm Hg
PCO = 45 mm Hg
Alveoli
CO
Nitrogen (P
n
2)
Oxygen (P
o2
)
Carbon dioxide (Pc02)
Other gases (P
o
,^
gases
)
Total:
597.4 mmHg (78.6%)
158.8 mmHg (20.9%)
0.3 mmHg (0.04%)
3.5 mmHg (0.46%)
760.0 mmHg (100%)
Alveolar air:
PO
2
O_
: 105 mm Hg
= 40 mm Hg
External respiration—Gas exchange
between alveoli and pulmonary
capillaries:
• Alveolar P0 greater than capillary P0
so 0 2 diffuses into capillary
• Alveolar PC0 less than capillary PC0,2
so C 02 diffuses out of capillary
Pulmonary capillaries
\
To lungs
To left atrium
To right atrium
To tissue cells
0xygenated blood:
P
0
= 100 mm Hg
P
C0
= 40 mm Hg
Internal respiration—Gas exchange
between systemic capillaries and
tissue cells:
• Capillary P0 greater than tissue P0
Systemic capillaries
Systemic tissue cells:
P0 = 40 mm Hg
PC0 = 45 mm Hg
C 02 exhaled
0 2 inhaled
so 0 2 diffuses into alveoli
P
CO
_
so 0 2 diffuses into tissue
Capillary PC0 less than tissue PC0
_
so C
0 2
diffuses out of tissue cells
Gases Are Exchanged at the Blood Capillaries 383
previous page 418 Craig Freudenrich, Gerard J  Tortora   Visualizing Anatomy and Physiology   2011 read online next page 420 Craig Freudenrich, Gerard J  Tortora   Visualizing Anatomy and Physiology   2011 read online Home Toggle text on/off